Refactoring in commit 66419bc0 (CTest: convert timeouts to
std::chrono::duration, 2017-11-20) changed out "infinite" timeout to a
value not representable by a 64-bit integer.  This causes undefined
behavior when e.g. KWSys Process converts the duration to a `long` to
interact with system APIs.  Use the old `1.0e7` maximum value.